The present application relates to medical devices and procedures, and to ultrasonic energy emitters adapted for use in such devices and procedures.
Contraction or xe2x80x9cbeatingxe2x80x9d of the heart is controlled by electrical impulses generated at nodes within the heart and transmitted along conductive pathways extending within the wall of the heart. Certain diseases of the heart known as cardiac arrhythmias involve abnormal generation or conduction of the electrical impulses. One such arrhythmia is atrial fibrillation or xe2x80x9cAFxe2x80x9d. Certain cardiac arrhythmias can be treated by deliberately damaging the tissue of the cardiac wall along a path crossing a route of abnormal conduction. This causes formation of a scar extending along the path where disruption occurred. The scar blocks conduction of the electrical impulses. Such a scar can be created by conventional surgery, but this entails all of the risks and expense associated with cardiac surgery. Another approach, described in Swartz et al., U.S. Pat. No. 5,575,766, is to introduce a catheter bearing a localized energy emitter such as an electrode for application of radio frequency (xe2x80x9cRFxe2x80x9d) energy at its distal tip into a heart chamber, such as the right or left atrium of the heart in the case of atrial fibrillation. The physician then moves the catheter so that the tip, and the localized emitter traces the desired path. In AF, the desired path typically is a closed loop encircling the openings or ostia of the pulmonary veins. RF energy applied through the electrode heats the tissue to a degree sufficient to cause death of the normal tissue and its replacement by scar tissue. Heating to this degree is referred to herein as xe2x80x9cablationxe2x80x9d. The elevated temperature required for ablation varies with the time of exposure to the elevated temperature, but heating to about 60-80xc2x0 C. is typically used. Tracing a precise path along the interior of a chamber in the heart of a living subject with the tip of a catheter involves inherent practical difficulties. Although curved guide wires can be placed within the catheter so that the catheter tip will tend to follow the guide wire as the physician moves it, the process is still difficult.
Swanson et al., U.S. Pat. No. 5,582,609 describes an elongated catheter having numerous RF electrodes disposed along its length in a distal region adjacent the tip. This distal region can be formed into a curved, looplike configuration and manipulated so that the electrodes lie along the desired path, whereupon RF energy is applied so as to ablate cardiac tissue. In a variant of this approach, the electrodes are mounted on a structure which opens to form a ring-like configuration. Even with these structures, however, it is difficult to assure the desired placement of the RF electrodes. Lesh, U.S. Pat. No. 5,971,983 describes an elongated catheter which is equipped with similar RF electrodes distributed over its distal region, and uses guide wires to position the distal region in place against the wall of the heart. Although this patent mentions a xe2x80x9cultrasonic element such as an ultrasound crystal elementxe2x80x9d along with numerous other devices as theoretically applicable to cardiac tissue ablation, it offers no structure for an elongated ultrasonic ablating device.
As described in various publications including Swartz, U.S. Pat. No. 5,938,660 and Lesh, International Publication WO 99/02096, the abnormal conduction routes in AF typically extend from the wall of the heart along the pulmonary veins. Therefore, AF can be treated by ablating tissue in a ring around each pulmonary vein at the juncture between the pulmonary vein and the heart. As described in the ""096 publication, such ablation can be performed by threading a catheter having a thermal ablation element at its distal tip into the heart so that the tip is lodged within the appropriate pulmonary vein. The catheter may bear a balloon which is inflated within the vein and which holds the catheter in place. The ablating element is then actuated so as to apply heat in a region surrounding the ablating element. In certain embodiments taught in the ""096 publication, the ablating element includes a radio frequency (xe2x80x9cRFxe2x80x9d) emitting element which is carried on the surface of the balloon. Ablation of the pulmonary vein using RF energy can create a rough, disrupted surface on the interior of the vein. This or other factors can lead to thrombosis or clot formation.
Other embodiments described in the ""096 publication disclose the use of ultrasonic transducers. The preferred ultrasonic transducer illustrated in the ""096 publication is a rigid ceramic piezoelectric element disposed on a catheter surrounded by a balloon. When the balloon is inflated, the piezoelectric element remains remote from the wall of the pulmonary vein. The piezoelectric element can be actuated to apply sonic energy through a fluid contained in the balloon, thereby heating the ring of vein wall tissue surrounding the balloon. As a further alternative, the ""096 publication shows an ultrasonic emitter in the form of a hollow concave disk. The ""096 publication suggests that such an emitter can be physically rotated around the axis of a catheter so as to ablate a ring-like zone. These transducers have numerous drawbacks even for use in ablation of a vein wall and are not adapted for ablation of the wall of the cardiac chamber.
Ultrasonic heating such as high intensity focused ultrasound (HIFU) is utilized for many therapeutic applications. As disclosed in commonly assigned International Application PCT/US98/1062, published as International Publication WO/98/52465 the disclosure which is hereby incorporated by reference herein, HIFU heating typically is conducted using an ultrasonic emitter having an array of transducers. The transducers are actuated with a drive signal so as to emit ultrasonic waves. The relative phasing of the waves is controlled by the physical configuration of the array and the phasing of the drive signal. These factors are selected so that the ultrasonic waves tend to reinforce one another constructively at a focal location. Tissue at the focal location is heated to a greater extent than tissue at other locations. As described, for example in copending, commonly assigned U.S. patent application Ser. No. 09/496,988, filed Feb. 2, 2000 and in the corresponding International application PCT/US00/02644 in copending, commonly assigned U.S. patent application Ser. No. 09/523,614 filed Mar. 22, 2000, and in the corresponding International application PCT/US00/07607 the disclosures of which are also incorporated by reference herein, HIFU may be applied by transducer arrays such as arrays of polymeric piezoelectric transducers. These arrays can be mounted on a probe such as a catheter which can be introduced into the body as, for example, within the vascular system or into a cavernous internal organ. The ""988 application discloses certain transducer arrays which can be deformed so as to vary the placement of the focal location.
One aspect of the invention provides apparatus for applying thermal treatment to tissue of an internal organ of a living subject. Apparatus according to this aspect of the invention desirably includes one or more catheters and an elongated energy emitter carried on one of the one or more catheters. The elongated energy emitter desirably is adapted to assume a desired shape when disposed within the interior of the organ. The apparatus desirably also includes an expansible positioning structure such as a balloon or other expansible element carried on one of the one or more catheters. When the energy emitter is in the desired curved shape, the energy emitter extends over the expansible positioning structure so that the expansible positioning structure can bias the elongated energy emitter against an interior wall of the organ. Thus, when the positioning element and energy emitter are in an operative condition, the energy emitter extends along an elongated path on the interior wall of the organ. The path has a shape corresponding to the desired shape of the energy emitter. The energy emitter desirably is operative to emit energy at a plurality of locations along its length so as to heat tissue surrounding the interior of the organ at a plurality of locations along the path.
Most preferably, the energy emitter is formed separately from the positioning element, so that the energy emitter can assume its desired shape before it is biased against the wall of the organ. The energy emitter may be adapted to assume a curved shape such as a substantially closed loop, so that the path along the interior wall of the organ will be generally in the form of a loop. The energy emitter desirably is adapted to emit energy substantially simultaneously at a plurality of locations along its length to thereby heat tissue at a plurality of locations along the path substantially simultaneously. In a particularly preferred arrangement, the energy emitter is an elongated ultrasonic transducer array.
The one or more catheters desirably include a treatment catheter carrying the energy emitter, the emitter extending lengthwise along the treatment catheter adjacent the distal end thereof. In a particularly preferred arrangement, the energy emitter is an elongated ultrasonic transducer array which is flexible in directions transverse to the lengthwise direction of the catheter to facilitate threading of the catheter into the body. The distal end of the treatment catheter, and hence the energy emitter, may be brought to the desired shape by structures within the catheter, or by additional elements such as curved guide wires or sheaths. The one or more catheters most preferably include a holding structure such as a stabilizer catheter separate from the treatment catheter, the holding structure carrying the expansible positioning element. The apparatus may include an anchor linked to the stabilizer catheter, the anchor being adapted to engage an anatomical structure in or adjacent said organ. The expansible positioning structure may be movable relative to the anchor while the anchor is engaged with said anatomical structure. For example, where the apparatus is used for treatment of atrial fibrillation or other cardiac arrhythmias, the treatment catheter bearing the energy emitter and the stabilizer catheter may be threaded into a chamber of the heart and the treatment catheter may be brought to the desired shape such as a generally loop-like configuration. The expansible positioning structure may be expanded and the anchor may be engaged in a pulmonary vein or other blood vessel, with the treatment catheter disposed between the positioning structure and the wall of the heart chamber. The positioning structure is urged toward the wall of the heart, so as to engage the energy emitter with the wall of the heart, as by moving the stabilizer catheter relative to the anchor. While the energy emitter is engaged with the wall of the heart, it is activated to apply energy and ablate tissue in the heart wall, thereby forming a lesion along a loop-like path. Desirably, the entire lesion can be formed without repositioning or reconfiguring the energy emitter.
A further aspect of the invention provides methods of applying thermal treatment to tissue of an internal organ of a living mammal. A method according to this aspect of the invention desirably includes the steps of inserting an elongated energy emitter into the interior of the internal organ and bringing the energy emitter to a desired shape in a desired position relative to the organ, inserting an expansible positioning element into the interior of the organ, and expanding the positioning structure so that the energy emitter is disposed between the positioning structure and the wall of the organ and the positioning structure biases the energy emitter against the interior wall of the organ. In this condition, the energy emitter extends along an elongated path on such interior wall having a shape corresponding to the desired shape of the energy emitter. While the energy emitter extends along this path, the energy emitter is actuated to emit energy at a plurality of locations along its length so as to heat tissue at a plurality of locations along the path. In a particularly preferred method, the entire lesion is formed in one actuation, or a few actuations, of the energy emitter, without repositioning or reconfiguring the emitter. Most preferably, the energy emitter is brought at least approximately to the desired shape and at least approximately to the desired position before the positioning structure is fully expanded and before the energy emitter is biased against the wall of the internal organ by the positioning element.
In a particularly preferred method, the energy emitter includes an array of one or more ultrasonic transducer elements, the array extending in a lengthwise direction, the one or more transducer elements emitting ultrasonic energy at plural locations along the length of the array. For example, the array may extend lengthwise along a treatment catheter as discussed above in connection with the apparatus. The use of ultrasonic energy allows formation of lesions in the wall with minimal damage to the lining of the wall. In ablation of heart tissue, this minimizes the possibility of thrombus formation. Most desirably, the method includes the step of focusing ultrasonic energy emitted by the one or more transducer elements onto a elongated focal region extending generally parallel to said path. The term xe2x80x9cfocusingxe2x80x9d as used in this disclosure with reference to sonic or ultrasonic energy, refers to providing such energy from spatially-separated regions of a transducer or transducer array such that the ultrasonic waves from plural spatially-separated regions of the transducer or transducer array converge with one another in passing from the transducer or array to a focal region and are in phase within one another within the focal region so that they mutually reinforce one another so as to provide a sonic power density in the focal region higher than the sonic power density at the transducer surface. Most typically, the focal region is disposed on or in the wall of the organ and has an area (measured in a plane normal to the direction of propulsion of the ultrasonic waves) smaller than the area of the transducer. The method may further include the step of varying the focus of the ultrasonic energy so as to move the focal region towards or away from the transducer or array and thereby position said focal region deeper or shallower within the wall of said organ while the array remains substantially in position along the path. The ability to focus the ultrasonic energy allows rapid heating of the tissue, and facilitates heating tissue in the focal region to the extent necessary to ablate it, while minimizing damage to adjacent tissues.
As discussed above in connection with the apparatus, the energy emitter desirably is flexible in directions transverse to its length. The step of inserting the energy emitter may include the step of advancing the array lengthwise through a tubular anatomical structure and then deforming the array in directions transverse to its lengthwise direction to the desired shape.
A further aspect of the invention provides a medical device including an elongated catheter body with proximal and distal directions in its direction of elongation and an elongated ultrasonic transducer array extending in the proximal and distal directions, the catheter body and the transducer array being flexible in all directions transverse to said proximal and distal directions.
Yet another aspect of the invention provides an elongated ultrasonic transducer array having lengthwise directions, the array including a sheetlike element having a first fold extending in the lengthwise directions of the array and defining a first pair of adjacent regions on opposite sides of the fold. These desirably are non-parallel with one another and non-coplanar with one another. For example, the first pair of adjacent regions may define a structure which is generally V-shaped when seen in cross-section with the viewing direction in the lengthwise direction of the array.
Most preferably, at least one of the regions in the first pair is an active region. The array includes a plurality of ultrasonic transducer elements disposed on or formed integrally with the sheetlike element in the active region or regions of such element. The sheetlike element has notches in each of the aforesaid regions, the notches extending along axes transverse to the first fold at locations spaced apart from one another in the lengthwise direction. The notches subdivide each of the regions into panes, the notches in each region of the first pair of adjacent regions being offset in the lengthwise direction of the array from the notches in the other region of such first pair of adjacent regions. Each pane of each region of said first pair has a hinge zone aligned with the axis of a notch in the other region of the first pair. The sheetlike element is flexible at least in the hinge zones. As further discussed below, this arrangement allows the array to bend in directions transverse to said lengthwise direction of the array, and typically allows bending in all directions transverse to the lengthwise direction. The sheetlike element desirably has one or more electrical conductors thereon, the conductors extending lengthwise along the sheetlike element in a zigzag pattern so that the conductors pass through the hinge regions of the panes and around the notches.
Yet another aspect of the invention provides a medical device including an elongated catheter body with proximal and distal directions in its direction of elongation, and an array as discussed above, the lengthwise directions of the array and the first fold extending in the proximal and distal directions of said body. The active region or regions desirably are disposed on or constitute an outwardly-facing surface of said body and extend in lateral directions transverse to said lengthwise directions.
Yet another aspect of the invention provides a medical ultrasonic applicator including a first elongated catheter body having an exterior surface and having proximal and distal directions; a distributed array of one or more ultrasonic transducer elements disposed on or constituting a portion of said exterior surface of said first body, the array extending in the proximal and distal directions; and an elongated lens overlying the array of transducer elements and extending in said proximal and distal directions, said lens being adapted to focus ultrasonic emissions from the transducer elements into a elongated focal region outside of said body but generally parallel thereto. Most preferably, the body, lens and array are flexible in directions transverse to the proximal and distal directions. The lens may include a hollow enclosure extending in the proximal and distal directions, the enclosure being filled with a lens fluid when the device is in an operative condition.
These and other objects, features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below, taken in conjunction with the accompanying drawings.